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Biomedical subjects

Joshua D Lambert

Publications and source records attributed to Joshua D Lambert.

At least 19 recordsLinked to original sources
PubMed2006

Wheat bran oil and its fractions inhibit human colon cancer cell growth and intestinal tumorigenesis in Apc(min/+) mice.

This study was designed to investigate the cancer preventive activities of wheat bran (WB) oil. We studied the colon cancer preventive effects of WB oil and its subfractions in the Apc(min/+) mouse model, a recognized mouse model for human colorectal cancer, and used human colon cancer cell lines (HCT-116 and HT-29) to identify possible active fractions in WB oil. Our results showed that the oil fraction of WB was more active than the water fraction against the growth of human colon cancer cell lines and that 2% WB oil significantly inhibited the overall tumorigenesis by 35.7% (p < 0.0001) in the Apc(min/+) mouse model. The WB oil was further fractioned into nonpolar lipids and phytochemicals and the phytochemical fraction was fractionated into phytosterols and phytosterol ferulates, 5-alk(en)ylresorcinols, and unidentified constituents by normal phase silica gel column chromatography. Results on cell culture showed that the phytochemical fraction had a higher inhibitory effect on HCT-116 human colon cancer cells than that of WB oil, whereas the nonpolar lipid fraction had less growth inhibitory effectiveness. However, neither fractions showed a stronger inhibition than WB oil in the Apc(min/+) mouse model. The current results demonstrate, for the first time, the intestinal cancer preventive activity of WB oil. The active ingredients, however, remain to be identified.

Animals↗
PubMed2006

Peracetylation as a means of enhancing in vitro bioactivity and bioavailability of epigallocatechin-3-gallate.

(-)-Epigallocatechin-3-gallate (EGCG) is the widely studied catechin in green tea (Camellia sinensis). Previously, we have reported the low bioavailability of EGCG in rats and mice. As a means of improving the bioavailability of EGCG, we have prepared a peracetylated EGCG derivative (AcEGCG) and herein report its growth inhibitory activity and cellular uptake in vitro, as well as bioavailability in mice. AcEGCG exhibited enhanced growth inhibitory activity relative to EGCG in both KYSE150 human esophageal (IC50 = 10 versus 20 microM) and HCT116 human colon cancer cells (IC50 = 32 versus 45 microM). AcEGCG was rapidly converted to EGCG by HCT116 cells, and treatment of cells with AcEGCG resulted in a 2.8- to 30-fold greater intracellular concentration of EGCG as compared with treatment with EGCG. AcEGCG was also more potent than EGCG at inhibiting nitric oxide production (4.4-fold) and arachidonic acid release (2.0-fold) from lipopolysaccharide-stimulated RAW264.7 murine macrophages. Intragastric administration of AcEGCG to CF-1 mice resulted in higher bioavailability compared with administration of equimolar doses of EGCG. The plasma area under the curve from 0 to infinity (AUC0-->infinity) of total EGCG was 465.0 and 194.6 [(microg/ml) . min] from the administration of AcEGCG and EGCG, respectively. The t1/2 of EGCG was also increased following administration of AcEGCG compared with EGCG (441.0 versus 200.3 min). The AUC0-->infinity and t1/2 were also increased in small intestinal (2.8- and 4.3-fold, respectively) and colonic tissues (2.4- and 6.0-fold, respectively). These data suggest that acetylation represents a means of increasing the biological potency in vitro, increasing the bioavailability of EGCG in vivo, and may improve cancer-preventive activity.

Acetates↗
PubMed2006

Molecular targets for the cancer preventive activity of tea polyphenols.

Inhibition of carcinogenesis by tea and tea polyphenols has been demonstrated in many animal models. The mechanisms of action have been extensively investigated mostly in cell culture systems with (-)-epigallocatechin-3-gallate (EGCG), the most active and major polyphenolic compound from green tea. However, the mechanisms of cancer preventive activity by tea and tea polyphenols are not clearly understood. This article discusses some of the reported mechanisms and possible targets for the action of EGCG. The difficulties and major issues in extrapolating data from studies in cancer cell lines to cancer prevention mechanisms are discussed. Activities observed in cell culture with high concentrations of EGCG may not be relevant because of the limited systemic bioavailability of EGCG. In addition, possible artifacts due to the auto-oxidation of EGCG may complicate this issue. Some recent studies revealed high-affinity EGCG binding proteins as possible direct targets for the action of EGCG. Validating the related cancer preventive mechanisms found in in vitro studies in animal models and human samples would be exciting.

Animals↗
PubMed2006

Possible mechanisms of the cancer-preventive activities of green tea.

The cancer-preventive activities of tea and some tea constituents, such as caffeine and (-)-epigallocatechin-3-gallate (EGCG), have been demonstrated in animal models. The mechanisms of action of the tea constituents have been extensively investigated, but the mechanisms for the cancer-preventive activity of tea are not clearly understood. This chapter discusses some of the reported studies on the green tea polyphenol, EGCG, and the major issues in the interpretation of these data. Among the different activities of EGCG observed in cell culture systems, we need to select the physiologically relevant ones based on the biological importance of the target as well as the effective concentration and whether the reaction can take place in vivo because of the limited bioavailability of EGCG. We also need to distinguish between primary and subsequent events. Possible artifacts should be recognized. The cancer-preventive mechanisms need to be validated in animal models or human samples.

Animals↗
PubMed2006

Transdermal delivery of (-)-epigallocatechin-3-gallate, a green tea polyphenol, in mice.

Epigallocatechin-3-gallate (EGCG) is the most studied catechin in green tea (Camellia sinensis). EGCG and green tea are cancer preventive in many animal models, and numerous mechanisms have been proposed in cell lines. EGCG is poorly bioavailable in man and rodents. We hypothesized that transdermal delivery of EGCG could result in improved bioavailability. Following application of EGCG transdermal gel (50 mg kg(-1), t.d.) to SKH-1 mice, EGCG was observed in the epidermis (1365.7-121.0 ng g(-1)) and dermis (411.2-42.6 ng g(-1)). The maximum plasma concentration (Cmax) of EGCG was 44.5 ng mL(-1). The t(1/2) (94.4 h) and AUC(0-->24 h) (881.5 ng mL(-1) h) of EGCG were greater than values previously reported for oral EGCG. The t(1/2) and area under the concentration-time curve up to 24 h (AUC(0-->24 h)) in the liver, small intestine and colon were 21.3-74.6 h and 715-2802 ng g(-1)h, respectively. Stability studies showed that the transdermal formulation was stable at 4 degrees C and had a half-life (t(1/2)) of 47.1 and 20.2 h at 25 degrees C and 37 degrees C, respectively. These data indicate that transdermal EGCG is useful for delivering prolonged levels of EGCG to plasma and tissues, and may provide an alternative to tea consumption as a dosage form of EGCG.

Administration, Cutaneous↗
PubMed2005

Dose-dependent levels of epigallocatechin-3-gallate in human colon cancer cells and mouse plasma and tissues.

Epigallocatechin-3-gallate (EGCG; molecular formula: C22H18011)is the most abundant catechin in green tea (Camellia sinensis Theaceae). Both EGCG and green tea have been shown to have cancer-preventive activity in a number of animal models, and numerous mechanisms have been proposed based on studies with human cell lines. EGCG has been shown to undergo extensive biotransformation to yield methylated and glucuronidated metabolites in mice, rats, and humans. In the present study, we determined the concentration-dependent uptake of EGCG by HT-29 human colon cancer cells (20-600 microM) and the dose dependence of EGCG plasma and tissue levels after a single dose of EGCG (50-2000 mg/kg i.g.) to male CF-1 mice. The cytosolic levels of EGCG were linear with respect to extracellular concentration of EGCG after treatment of HT-29 cells for 2 h (915.3-6851.6 microg/g). In vivo, EGCG exhibited a linear dose relationship in the plasma (0.03-4.17 microg/ml), prostate (0.01-0.91 microg/g), and liver (0.09-18.3 microg/g). In the small intestine and colon, however, the levels of EGCG plateaued between 500 and 2000 mg/kg i.g. These results suggest that absorption of EGCG from the small intestine is largely via passive diffusion; however, at high concentrations, the small intestinal and colonic tissues become saturated. The levels of 4''-O-methyl-EGCG and 4',4''-di-O-methyl-EGCG parallel those of EGCG with respect to dose. The present study provides information with respect to what concentrations of EGCG are achievable in mice and may guide dose selection for future cancer chemoprevention studies with EGCG.

Administration, Oral↗
PubMed2005

Inhibition of human liver catechol-O-methyltransferase by tea catechins and their metabolites: structure-activity relationship and molecular-modeling studies.

(-)-Epigallocatechin-3-gallate (EGCG) is the major polyphenol present in green tea. We previously demonstrated that EGCG was both a substrate and potent inhibitor of human liver cytosolic catechol-O-methyltransferease (COMT). We now report the structure-activity relationship for the inhibition of COMT-catalyzed O-methylation of catecholestrogens in human liver cytosol by tea catechins and some of their metabolites. The most potent inhibitors were catechins with a galloyl-type D-ring, including EGCG (IC(50)=0.07 microM), 4''-O-methyl-EGCG (IC(50)=0.10 microM), 4',4''-di-O-methyl-EGCG (4',4''-DiMeEGCG) (IC(50)=0.15 microM), and (-)-epicatechin-3-gallate (ECG) (IC(50)=0.20 microM). Catechins without the D-ring showed two to three orders of magnitude less inhibitory potency. Enzyme kinetic analyses revealed that EGCG behaved as a mixed inhibitor, whereas 4',4''-di-O-methyl-EGCG exhibited competitive kinetics for the S-adenosylmethionine (SAM), and noncompetitive kinetics for the catechol binding site. These compounds may represent a new type of COMT inhibitor. In silico molecular-modeling studies using a homology model of human COMT were conducted to aid in the understanding the catalytic and inhibitory mechanisms. Either D-ring or B-ring of EGCG could be accommodated to the substrate binding pocket of human COMT. However, the close proximity (2.6A) of 4''-OH to the critical residue Lys144, the higher acidity of the hydroxyl groups of the D-ring, and the hydrophobic interactions between the D-ring and residues in the binding pocket greatly facilitated the interaction of the D-ring with the enzyme, and resulted in increased inhibitory potency. These results provide mechanistic insight into the inhibition of COMT by commonly consumed tea catechins.

Catechin↗
PubMed2005

Benzotropolone inhibitors of estradiol methylation: kinetics and in silico modeling studies.

Natural and synthetic benzotropolone compounds were assessed in vitro for their ability to inhibit hydroxyestradiol methylation by catechol-O-methyltransferase (COMT). The compounds were also modeled in silico with a homology model of human COMT. Purpurogallin (1), purpurogallin carboxylic acid (2), and theaflavin-3,3'-digallate (6) were the most potent inhibitors of 2-hydroxy and 4-hydroxyestradiol methylation (IC(50) 0.22-0.50microM). Compounds 1 and 6 decreased the V(max) and increased the K(m) of COMT, indicating a mixed-type inhibition. Compounds 1 and 2 bound to COMT by inserting the six-membered ring of the benzotropolone into the active site. Decreased acidity of the hydroxyl groups on this ring or increased bulkiness reduced potency. Compound 6 bound by inserting the galloyl ester into the active site, which allowed the compound to overcome increased bulkiness and resulted in restored potency. Further studies are needed to determine the impact in vivo of COMT inhibition by these compounds.

Catechol O-Methyltransferase Inhibitors↗
PubMed2005

Synthesis and biological activity of the tea catechin metabolites, M4 and M6 and their methoxy-derivatives.

Syntheses are reported for metabolites M4 (1) and M6 (2) of the green tea polyphenols epicatechin (EC) and epigallocatechin (EGC) and their gallate derivatives. Several methoxy-derivatives of 1 and 2 were also prepared. Compounds 1 and 2 were evaluated for growth inhibitory activity against a panel of immortalized and malignant human cell lines with 1 being the more active compound. The possible antiinflammatory activity of 1 and its trimethoxy derivative was also evaluated. Neither compound inhibited the release of arachidonic acid, although 1 inhibited NO production by 50% at 20 microM.

Animals↗
PubMed2005

Cytotoxic lignans from Larrea tridentata.

Six lignans, including the cyclolignan 3,4'-dihydroxy-3',4'-dimethoxy-6,7'-cyclolignan, were isolated from the flowering tops of Larrea tridentata. Additionally the flavanone, (S)-4',5-dihydroxy-7-methoxyflavanone, was isolated for the first time from L. tridentata or any member of the family Zygophyllaceae. All of the compounds were assessed for their growth inhibitory activity against human breast cancer, human colon cancer and human melanoma cell lines. The lignans had IC50 values of 5-60 microM with the linear butane-type lignans being the most potent, and it was found that colon cancer cells were the least sensitive cell type tested. The relative potency of linear butane type lignans against human breast cancer appears to correlate positively with the number of O-methyl groups present on the molecule.

Antineoplastic Agents, Phytogenic↗
PubMed2005

Synthesis and structure identification of thiol conjugates of (-)-epigallocatechin gallate and their urinary levels in mice.

(-)-Epigallocatechin gallate (EGCG), the most abundant and most biologically active compound in tea, has been proposed to have many beneficial health effects. The metabolic fate of EGCG, however, is not well understood. In the present study, we found that EGCG can be oxidized by peroxidase and hydrogen peroxide and then reacted with cysteine or glutathione to form conjugates. The structures of the cysteine and glutathione conjugates of EGCG were identified using 2D NMR and MS. Two thiol conjugates of EGCG (2'-cysteinyl EGCG and 2' '-cysteinyl EGCG) were identified by ESI-LC-MS/MS analysis from the urine samples of mice administered 200 or 400 mg/kg EGCG, i.p. These conjugates were not found in urine samples of mice after receiving EGCG at 50 mg/kg i.p., or 2000 mg/kg i.g., or in human urine following consumption of 3 g of decaffeinated green tea solids (containing 333 mg EGCG). At high doses, EGCG is believed to be oxidized to form EGCG quinone, which can react with glutathione to form the thiol conjugates. These results suggest that detectable amounts of thiol conjugates of EGCG are formed only after rather high doses of EGCG are given to the mice.

Adult↗
PubMed2005

Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations.

Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo. For example, compounds such as curcumin are effective when applied topically to the skin or administered orally to affect the colon but are not effective in internal organs such as the lungs. More in-depth studies on bioavailability should facilitate correlation of mechanisms determined in vitro with in vivo situations, increase our understanding of dose-response relationships, and facilitate extrapolation of results from animal studies to human situations.

Animals↗
PubMed2004

Effects of tea polyphenols on signal transduction pathways related to cancer chemoprevention.

The inhibition of carcinogenesis by tea and tea polyphenols has been demonstrated in different animal models by many investigators. The mechanisms of this inhibitory activity have also been investigated extensively, mostly in cell culture systems, but no clear conclusion can be reached concerning the cancer preventive mechanisms in vivo. In this article, we reviewed the possible mechanisms, which include the inhibition of specific protein kinase activities, blocking receptor-mediated functions, and inhibition of proteases. These events may lead to cell cycle regulation, growth inhibition, enhanced apoptosis, inhibition of angiogenesis, and inhibition of invasion and metastases. The possible complications of translating results obtained in cell culture studies to animals and humans are discussed. It is likely that multiple signal transduction pathways are involved in the inhibition of carcinogenesis by tea constituents. The relative importance of these pathways needs to be determined in vivo.

Animals↗
PubMed2004

Enzymatic synthesis of tea theaflavin derivatives and their anti-inflammatory and cytotoxic activities.

Derivatives based on a benzotropolone skeleton (9-26) have been prepared by the enzymatic coupling (horseradish peroxidase/H2O2) of selected pairs of compounds (1-8), one with a vic-trihydroxyphenyl moiety, and the other with an ortho-dihydroxyphenyl structure. Some of these compounds have been found to inhibit TPA-induced mice ear edema, nitric oxide (NO) synthesis, and arachidonic acid release by LPS-stimulated RAW 264.7 cells. Their cytotoxic activities against KYSE 150 and 510 human esophageal squamous cell carcinoma and HT 29 human colon cancer cells were also evaluated.

Animals↗
PubMed2004

Piperine enhances the bioavailability of the tea polyphenol (-)-epigallocatechin-3-gallate in mice.

(-)-Epigallocatechin-3-gallate (EGCG), from green tea (Camellia sinensis), has demonstrated chemopreventive activity in animal models of carcinogenesis. Previously, we reported the bioavailability of EGCG in rats (1.6%) and mice (26.5%). Here, we report that cotreatment with a second dietary component, piperine (from black pepper), enhanced the bioavailability of EGCG in mice. Intragastric coadministration of 163.8 micromol/kg EGCG and 70.2 micromol/kg piperine to male CF-1 mice increased the plasma C(max) and area under the curve (AUC) by 1.3-fold compared to mice treated with EGCG only. Piperine appeared to increase EGCG bioavailability by inhibiting glucuronidation and gastrointestinal transit. Piperine (100 micromol/L) inhibited EGCG glucuronidation in mouse small intestine (by 40%) but not in hepatic microsomes. Piperine (20 micromol/L) also inhibited production of EGCG-3"-glucuronide in human HT-29 colon adenocarcinoma cells. Small intestinal EGCG levels in CF-1 mice following treatment with EGCG alone had a C(max) = 37.50 +/- 22.50 nmol/g at 60 min that then decreased to 5.14 +/- 1.65 nmol/g at 90 min; however, cotreatment with piperine resulted in a C(max) = 31.60 +/- 15.08 nmol/g at 90 min, and levels were maintained above 20 nmol/g until 180 min. This resulted in a significant increase in the small intestine EGCG AUC (4621.80 +/- 1958.72 vs. 1686.50 +/- 757.07 (nmol/g.min)). EGCG appearance in the colon and the feces of piperine-cotreated mice was slower than in mice treated with EGCG alone. The present study demonstrates the modulation of the EGCG bioavailablity by a second dietary component and illustrates a mechanism for interactions between dietary chemicals.

Alkaloids↗
PubMed2004

Delivery of tea polyphenols to the oral cavity by green tea leaves and black tea extract.

Catechins and theaflavins, polyphenolic compounds derived from tea (Camellia sinensis, fam. Theaceae), have been reported to have a wide range of biological activities including prevention of tooth decay and oral cancer. The present study was undertaken to determine the usefulness of green tea leaves and black tea extract for the delivery of catechins and theaflavins to the oral cavity. After holding either green tea leaves (2 g) or brewed black tea (2 g of black tea leaves in 100 ml) in the mouth for 2-5 min and thoroughly rinsing the mouth, high concentrations of catechins (C(max) = 131.0-2.2 micro M) and theaflavins (C(max) = 1.8-0.6 micro M) were observed in saliva in the 1st hour. Whereas there was significant interindividual variation in the peak levels of catechins and theaflavins, the overall kinetic profile was similar, with t(1/2) = 25-44 min and 49-76 min for catechins and theaflavins, respectively (average coefficient of variation in t(1/2) was 23.4%). In addition to the parent catechin and theaflavin peaks, five unidentified peaks were also observed in saliva after black tea treatment. Hydrolysis of theaflavin gallates, apparently by salivary esterases, was observed in vitro and in vivo. These results indicate that tea leaves can be used as a convenient, slow-release source of catechins and theaflavins and provide information for the possible use of tea in the prevention of oral cancer and dental caries.

Adult↗
PubMed2003

Involvement of multidrug resistance-associated proteins in regulating cellular levels of (-)-epigallocatechin-3-gallate and its methyl metabolites.

(-)-Epigallocatechin-3-gallate (EGCG), a major polyphenol of green tea, has many interesting biological activities. The uptake of EGCG and involvement of specific efflux pumps were studied in MDCKII cells transfected with hPgp, hMRP1, and hMRP2 genes. Total cell associated [3H]EGCG increased 7-fold in the presence of the MRP inhibitors, indomethacin and probenecid, in MDCKII/MRP1 cells, compared to a 2-fold increase in wild-type cells. Intracellular levels of EGCG, 4(")-O-methyl EGCG, and 4('),4(")-di-O-methyl EGCG were increased by 13-, 11-, and 3-fold, respectively, by indomethacin in MDCKII/MRP1 cells. Accumulation of EGCG and its methyl metabolites was also increased approximately 10-fold in the presence of MK-571 in MDCKII/MRP2 cells. Co-treatment with isoflavones, curcumin and tetrahydrocurcumin, increased [3H]EGCG accumulation significantly in MDCKII/MRP1 and HT-29 cells. The results indicate that EGCG and its methyl metabolites are substrates for MRP1 and MRP2, but not for Pgp. MRP type efflux pumps may limit the bioavailability of EGCG.

Animals↗